Relative Humidity and Temperature Sensing Characteristics of an Optical Fiber Probe Based on Hollow-Core Fiber and Calcium Alginate Hydrogel Film

Hydrogel is a kind of functional cross-linked polymer material with 3-D network structure. When hydrogel is exposed to water environment, a mass of hydrophobic groups and hydrophilic residues existing in the cross linked netlike nano-structure is willing to combine with water molecules and expand, respectively. In this paper, a novel optical fiber probe based on hollow-core fiber and calcium alginate (CaAlg) hydrogel film is proposed and experimentally demonstrated. The experimental results of relative humidity (RH) and temperature sensing characteristics show that the proposed probe has a binomial response to RH in the range of 20%similar to 90% RH and a linear response to temperature with the sensitivity of 121pm/degrees C. CaAlg is considered as an effective and potential as the humidity-sensitive material to optical fiber RH sensors.